antique radio 'tuning capacitor'

This is an example of a "variable capacitor" ('variable condenser' in its day) in terms of electronic componentry. By today's household standard it is a ridiculously *large* specimen physically, but that wasn't so true +/- a hundred years ago when this exact part served as the component on the other side of the TUNING knob inside a large wooden cased console radio -- the plastic indicator that would have shown which frequencies (radio stations) were tuned in (backlit, thru a fancy bezel plate amongst the controls) is still on its end along with a now broken slender cloth cord that connected it all together to the knob itself. (pics 2 & 4)

Physically, it consists of four sets of vaguely crescent-shaped aluminum plates, half of which are stationary while the other half are attached to a lengthwise axle and can rotate (together) into or out of the spaces between the fixed ones, without actually touching them anywhere. (they are moved to different positions in pics 1 & 3)

And when you put a thing like this inbetween a whole bunch more other little electrical gizmos and whatzits (technical terms, those...!) hooked up every which way, then actually rotate it, you get a RADIO and this thing TUNES IN the stations?!! :-) :-) :-) :-) :-)

In the intervening hundred years (up to the advent of 'digital radio' anyway) the electrical theory behind this thing didn't change much at all, though the specific forms of the device became sub-miniature tiny when needed or required. There are also many, many other electrical applications for a device similar to this, up to and including much larger examples in industrial equipment, where I believe things like it can be found helping to regulate really large sources of electricity in things like power plants and substations.

I don't remember much about the radio itself that this one was used in -- other than that it was an "old, junk" radio that probably didn't work anymore already when it was given to me as a young teenager, specifically so I could amuse myself by taking it all apart to find out what was inside everything...maybe it truly gave its life to a noble (??) cause way back then vs. just being hauled to a dump, but with my 'today eyes' I *certainly* wish I had much more of the whole thing now...I do remember it was old enough to have had a fancy 'box on legs' cabinet and 'coke bottle' tubes...could have easily been 1920's... <groan>